Stress Intensity Flashcards
(11 cards)
What is the magnification known as?
The stress concentration factor
What are the two criteria for crack propagation in the Griffith criteria?
For thin samples : Plane stress dominates
For thick Samples: Plane strain dominates
What is the main variable between all stress analysis equations for the strength of a ceramic to be solely reliant on?
The strength of a ceramic is dependent on its largest flaw in the stressed region,
irrespective of any other flaws – provided that there is no interaction between flaws. i.e. c
What are the 3 modes of the Irwin formulation?
Mode I- Crack opening - driven by tensile stress normal to crack (crack faces are pulled apart perpendicularly to the crack plane
Mode II-in plane crack shearing or sliding - cause from in plane shear stress- cracks slide over each other in the plane of the crack, perpendicular to the crack front
Mode III- antiplane crack shearing or tearing - cause by out of plane shear stress - crack faces slide relative to each other in the plane of crack
What is the stress intensity factor?
known as Km, a function of crack (flaw) depth and applied stress. completely characterises the crack tip conditions in a linear elastic material.
Stress Intensity Factor could explain any combination of the effects of specimen shape, external loading, and crack configuration that could lead crack propagation.
for ceramics why do you think that only KI for Mode I of Irwins formulations can be used?
Mode I is the most common in real life. There is clearer fracture criteria for Mode I and Mode I tends to be the most dominant compared to the other modes even if al 3 are there
When measuring the materials resistance to brittle fracture, how can the stress intensity factor and fracture toughness be equated?
The fracture toughness becomes equal to the stress intensity so that either the crack depth or critical stress can be found or the max allowable flaw size can be determined.
What are the 2 main approaches of fracture analysis?
Either through energy or stress intensity
What are the 3 main variables to be quantified through structure mechanics?
1- Stress
2- Flaw size
3- Fracture toughness
What is the energy release rate?
the amount of energy available per unit of new crack surface
How can the energy release rate be related to the stress intensity factor?
The energy release rate(G) can be equal to the crack resistance force R. So Griffiths energy based criterion is related to Irwins stress based criterion where G= Ki^2/E or = Ki^2/E*(1-V^2) for plane stress or strain respectively. v is the poissions ratio(strain transverse / strain longitudinal). This is the relationship of a mechanical(intensity of stress) and thermodynamic view(energy).
